1. Field of the Invention
This invention relates to a seat slide adjuster for vehicles, particularly a seat slide adjuster having a bracket for attachment to a seat belt on an upper rail slidable with respect to a lower rail fixed to a vehicle body.
2. Descrption of the Prior Art
Recently, a local regulation requests to install a seat belt for the sake of safety so that an easy handling of the seat belt is desired. In the meantime, it has been normal to slide a seat in fore and aft direction to establish a comfortable attitude of the seated individual. In this case, when the ends of the seat belt are fastened to the vehicle body, the arrangement of the seat belt is substantially disturbed by sliding movement of the seat in retain to the vehicle body. When at least one end of the seat belt is fastened to a bracket of a seat slide adjuster allowing the free sliding movement of the seat, a proper tension of the belt is kept while the seat position is adjusted.
To enable the seat to be adjustable in the fore and aft direction and at least one end of the seat belt to be fastened to the seat slide adjuster, a seat reclining hinge pin and a seat belt anchorage are secured to the bracket of the seat slide adjuster so that a high stripping load is applied to an upper rail having the bracket for attachment to the seat belt in a collision and the upper rail is torn away from a lower rail fixed to the vehicle body or floor. The local regulation required to mount the seat slide adjuster of a high strength to withstand such the high stripping load in the collision.
To prevent the upper rail from being torn away from the lower rail when the uppwardly directed stripping load is received by the upper rail, in a conventional seat slide adjuster the configuration of the rail is to be improved and the thickness of the rail is to be increased.
For example, the specification of EP076041, the specification of British Patent No. 1524952 or the specification of Japanese Patent Application Laid-Open (Kokai) No. 62-238136 discloses an improved seat slide adjuster, respectively. A conventional or typical attempt to improve the strength of a seat slide adjuster is illustrated in FIGS. 6, 7 and 8. The seat slide adjuster has a low rail 2 fixed through fittings 10, 11 to a vehicle floor and an upper rail 1 to which a seat cushion frame is attached. The upper rail 1 is located in such a manner that sliding movement of the upper rail 1 relative to the lower rail 2 in the longitudinal direction is possible. A hinge plate 4 is secured to a rear end of the upper rail 1 and has a seat reclining hinge pin 5 for holding the seat cushion and a seat belt anchorage 3.
As shown in FIGS. 7 and 8, the upper rail 1 has a generally inverted T-shaped cross section and comprises L-shaped metal plates opposed each other. A horizontal surface 24 of each metal plate is provided with a vertical flange 15. The lower rail 2 has a generally C-shaped cross section and horizontal surfaces 16 thereof are provided with downwardly extendings flanges 17, respectively. Each upper surface 16 is opposed to each lower surface 24 in spaced relation and each vertical flange 15 is opposed to each downward flange 17 in spaced relation to define a track for balls 13. Rollers 14 are located between a base portion 20 and the lower surfaces 24.
Since a heavy load is applied to the seat belt anchorage 3, bending stresses are generated at corner portions 18, 19 so that a reinforcement thereof is necessary. In an example of FIG. 8, reinforcement plates 29, 30 are attached to the lower surfaces 24 and the corners 19. This will be heavy in weight and increase the number of parts.
For holding the upper rail 1 relative to the lower rail 2 after adjustment of fore and aft position of the seat a lack mechanism 28 is used.